Micro-Coil Design Influences the Spatial Extent of Responses to Intracortical Magnetic Stimulation

• Published in: IEEE transactions on biomedical engineering Vol. 66; no. 6; pp. 1680 - 1694
• Main Authors: Lee, Seung Woo, Thyagarajan, Krishnan, Fried, Shelley I.
• Format: Journal Article
• Language: English
• Published: United States IEEE 01-06-2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Activation; Animals; Axons; Axons - physiology; Axons - radiation effects; Brain; Brain modeling; Brain slice preparation; Calcium; Calcium imaging; Coils; Computational neuroscience; Computer Simulation; Design; Electric fields; Electrical stimuli; Electrodes; Equipment Design; Implanted electrodes (biology); intracortical magnetic stimulation primary visual cortex (V1); intracortical micro-coil; Magnetic fields; Magnetic stimulation; Mice; Mice, Inbred C57BL; Micro-magnetic stimulation (µMS); Neural Prostheses; neural prosthesis; Neuroimaging; Neurological diseases; Neurons; Prosthetics; Pyramidal cells; Recording; Selectivity; Shape; Stimulation; Substrates; Transcranial Magnetic Stimulation - instrumentation; Transcranial Magnetic Stimulation - methods; Visual Cortex - cytology; Visual Cortex - radiation effects
• ISSN: 0018-9294; 1558-2531
• DOI: 10.1109/TBME.2018.2877713

Objective: Electrical stimulation via cortically implanted electrodes has been proposed to treat a wide range of neurological disorders. Effectiveness has been limited, however, in part due to the inability of conventional electrodes to activate specific types of neurons while avoiding other types. Recent demonstrations that magnetic stimulation from a micro-coil can selectively activate pyramidal neurons (PNs) while avoiding passing axons suggest the possibility that such an approach can overcome some this limitation and here we use computer simulations to explore how the micro-coil design influences the selectivity with which neurons are activated. Methods: A computational model was developed to compare the selectivity of magnetic stimulation induced by rectangular-, V-, and W-shaped coil designs. The more promising designs (V- and W-shapes) were fabricated for use in electrophysiological experiments including in vitro patch-clamp recording and calcium imaging (GCaMP6f) of mouse brain slices. Results: Both V- and W-shaped coils reliably activated layer 5 (L5) PNs but V-coils were more effective while W-coils were more selective. Activation thresholds with double-loop coils were approximately one-half those of single-loop coils. Calcium imaging revealed that both V- and W-coils better confine activation than electrodes. Conclusion: Individual design features can influence both the strength as well as the selectivity of micro-coils and can be accurately predicted by computer simulations. Significance: Our results show that how coil design influences the response of cortical neurons to stimulation and are an important step toward the development of next-generation cortical prostheses.